Radiological assessment of the limits and potential of reduced activation ferritic/martensitic steels

•Ni is the major contamination element that should be removed to reduce the activation levels.•The amount of 14C transmuted from N must be reduced to achieve the shallow land burial limit.•About 100ppm N will remain in the EAF melted steel, and Ni contamination occurs during the melting process.•Using Al for deoxidation of the RAFM steel has no significant impact on the activation levels.•The impact of the minor elements such as Ag is negligible compared to that of Ni and N. Reduced activation ferritic/martensitic (RAFM) steels have been developed as the structural material for the fusion demonstration reactor, DEMO. These steels contain elements that produce radioactive isotopes and decay to low levels in timeframe required by the waste management scenario. Developments within the past quarter-century suggest a practical limit to the removal of undesired impurities such as Co, Cu, Ni, Mo and Nb. The concentrations of elements essential for the mechanical properties of RAFM steels, such as Al and N, required a compromise between the waste disposal scenario and performance demand. The limits and potential of RAFM steel pertaining to reducing the activation levels after service are discussed based on the actual achievements of F82H, Japanese RAFM steel, and numerical analyses of the activity. It was found that in order to achieve the shallow land burial limits 100 years after a reactor shutdown, Ni is the most significant impurity that must be removed (Mo in the case of the first wall). Limiting N below concentrations of 100ppm will not be possible for a large scale melt, but concentrations of Al up to the maximum amount that has been achieved present no problems.